Diisopropenylbenzene is a monomer that can be used in the preparation of useful polymers and is also a chemical intermediate that can be used in a number of chemical processes. Diisopropenylbenzene can be synthesized by the dehydrogenation of diisopropylbenzene. For example, meta-diisopropylbenzene (m-DIPB) can be dehydrogenated into meta-diisopropenylbenzene (m-DIB) and para-diisopropylbenzene (p-DIPB) can be dehydrogenated into para-diisopropenylbenzene (p-DIB). Unfortunately, in this dehydrogenation process some olefinic impurities are produced as by-products. These olefinic impurities include isopropylstyrene, divinylbenzene, isopropenyl styrene, and other similar organic impurities. Obviously, it would be very desirable to remove these impurities from the meta- or para-diisopropenylbenzene produced by the dehydrogenation of diisopropylbenzene.
It was believed that meta- or para-diisopropenylbenzene could be removed from these organic impurities by fractional distillation. However, when fractional distillations were attempted the contents of the distillation pot (p-DIB or m-DIB and the organic impurities) polymerized into a gel at the elevated temperature needed for the distillation making it impossible. This polymerization even takes place with as much as 1,000 ppm (parts per million) of polymerization inhibitor present in the distillation pot with gel formation long before all of the diisopropenylbenzene can be recovered.
Sometimes unwanted by-products can be removed by hydrogenation. For example, U.S. Pat. Nos. 3,887,632, 3,912,789, and 3,922,318 show that acetylenes can be removed from a stream containing butadiene and/or isoprene by selective hydrogenation.